Reduction-oxidation photocycle dynamics of flavins in starch films |
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Authors: | Alfons Penzkofer |
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Affiliation: | Faculty of Physics, University of Regensburg, Universitaetsstrasse 31, D-93053 Regensburg, Germany; E-Mail: alfons.penzkofer@physik.uni-regensburg.de ; Tel.: +49-941-943-2107; |
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Abstract: | The blue-light photo-reduction (conversion of oxidized flavin quinone via flavin semiquinone to fully reduced flavin hydroquinone) and dark re-oxidation of the flavins riboflavin and lumiflavin in starch (α-amylose) films was studied by absorption and luminescence spectroscopy. Blue-light photo-excitation caused an absorption, fluorescence, and phosphorescence decrease which recovered in the dark. The photo-reduction dark-oxidation cycle could be repeated. The efficiency of photo-reduction decreased with exposed excitation energy, and the speed of re-oxidation in the dark slowed down with time after excitation. The absorption did not fully recover. The fluorescence efficiency after a long time of storage in the dark increased beyond the initial flavin quinone fluorescence efficiency. Flavin photo-excitation is thought to cause starch-flavin restructuring (static fluorescence quenching center formation), enabling enhanced photo-induced starch to flavin electron transfer with subsequent flavin reduction and starch oxidation. In the dark, after light switch-off, thermal reversion of flavin reduction and starch oxidation occurred. |
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Keywords: | riboflavin lumiflavin starch oxystarch flavin photo-reduction cycle starch photo-oxidation cycle static fluorescence quenching photo-induced starch restructuring phosphorescence delayed fluorescence |
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